
Following the links, I discovered that one of the first versions was developed by Mike Mayfield in 1972 for the HP2000C computer. Subsequently, it was published by David H. Ahl in the book "BASIC Computer Games", receiving several additions. After finding a text listing of the game, I decided to take the challenge for myself and convert it in full to the ZX81.
The result I present here, fully functional and interactive! The disadvantage is that because it is in BASIC, the processing is too slow and I had to use FAST mode to speed up the heavier processing (for Zeddys equipped with Andy's ZXULA2, it's recommended to activate the Turbo mode before loading the game. All FAST instructions in the game are already followed by the respective "POKE 1001, x").
The game requires at least 32Kb of RAM, which will not be a problem for ZXpand owners. There are two programs: the first contains the game instructions and is also responsible for setup the RAMTOP to value 49152 before load the second program, the game itself.
I hope you like it, I particularly found the game really fun!